1. Field of the Invention
The present invention relates to a ceramic electronic component including a baked external electrode formed by baking a conductive paste onto a ceramic body, and a plated external electrode on the surface of the baked external electrode, more particularly, to a ceramic electronic component in which a glass layer derived from a glass material included in a conductive paste is located on the surface of a ceramic body near an outer edge of a baked external electrode.
In addition, the present invention relates to a method for manufacturing a ceramic electronic component.
2. Description of the Related Art
For ceramic electronic components, conductive pastes may be baked onto ceramic bodies to form baked external electrodes, and plated external electrodes may be further formed by plating on the surfaces of the baked external electrodes. The plated external electrodes are formed for the purpose of, for example, improving solderability for mounting, or protecting the baked external electrodes.
For example, in the case of a plated external electrode with a first layer composed of a Ni layer and a second layer composed of a Sn layer from a baked external electrode, the Ni plated layer for the first layer protects the baked external electrode from so-called solder corrosion, and the Sn plated layer for the second layer contributes to improved solderability.
In this regard, plating steps for ceramic electronic components are typically carried out by electrolytic plating, and the plating solutions used are often strongly acidic.
In such plating steps, in the case of ingress of the strongly acidic plating solutions between the ceramic bodies and the baked external electrodes, the solutions erode the ceramic bodies just below outer edges of the baked external electrodes. Moreover, when water adheres to the eroded portions for some reason while using the eroded ceramic electronic components mounted on electronic devices, the metals of the external electrodes are ionized to cause migration in a direction of electric field.
There has been a possibility that the migration will serve as discharge paths to cause short-circuits, and thus break the ceramic electronic components.
In addition, in the ceramic electronic components, the ceramic bodies may be conductive, for example, like thermistors. Further, in the case of forming plated external electrodes for such conductive ceramic bodies, plated films may adhere to not only the surfaces of the plated external electrodes, but also the surfaces of the ceramic bodies, to which the films really should not adhere. Further, when the external electrodes are connected with the plated films adhering to the surfaces of the ceramic bodies, there is a possibility that the external electrodes will be short-circuited to cause defects.
Therefore, for conventional ceramic electronic components, in plating steps, various efforts have been made so as to keep portions of ceramic elements just below outer edges of baked external electrodes from being eroded by plating solutions, and so as to keep plated films from adhering to the surfaces of the ceramic elements even when the ceramic elements are conductive.
For example, the ceramic electronic component (conductive chip-type ceramic element) 300 described in JP 5-251210 A is manufactured by the following method.
First, an unfired ceramic body 101 is prepared as shown in FIG. 7A.
Next, as shown in FIG. 7B, the unfired ceramic body 101 is subjected to firing to obtain a fired ceramic body 102.
Next, as shown in FIG. 7C, an insulating inorganic layer 103 of 0.1 μm to 2 μm in thickness, which is composed of a SiO2 film, a thin film of oxides such as SiO2 and Al2O3, or a thin film of glass containing, as its main constituent, an oxide such as SiO2, is formed over the entire surface of the fired ceramic body 102 by a physical vapor deposition method (PVD method) or a chemical vapor deposition method (CVD method), such as a vacuum deposition method, a sputtering method, or an ion plating method. This inorganic layer 103 is required to have a higher melting point or softening point than a firing temperature in the case of forming baked electrodes as will be described later.
Next, as shown in FIG. 7D, a conductive paste 104 including a metal powder such as Ag or Au and an inorganic binder is applied by a dipping method or the like to the surfaces of both ends of the ceramic body 102 with the inorganic layer 103 formed over the entire surface. Examples of the inorganic binder include glass microparticles such as borosilicate based glass, zinc borate based glass, cadmium borate based glass, and lead zinc silicate based glass, which contain an oxide such as SiO2 as their main constituent. The inorganic binder is uniformly dispersed in the conductive paste 104 applied.
Next, as shown in FIG. 7E, the conductive paste 104 applied to the surfaces of the both ends of the ceramic body 102 is baked to form baked external electrodes (baked electrode layers) 105. In this case, the inorganic binder in the conductive paste 104 reacts the inorganic substance layer 103 in contact with the conductive paste 104 to melt the inorganic substance layer 103. Then, the melted inorganic substance layer 103 is incorporated into the conductive paste 104. This results in the absence of the inorganic substance layer 103 between the ceramic body 102 and the baked external electrodes 105.
Next, as shown in FIG. 7F, Ni plated external electrodes (Ni plated layers) 106 are formed on the surfaces of the baked external electrodes 105.
Finally, as shown in FIG. 7G, Sn plated external electrodes (Sn plated layers) 107 are formed on the surfaces of the Ni plated external electrodes 106 to complete the conventional ceramic electronic component 300.
In the formation of the Ni plated external electrodes 106 and the formation of the Sn plated external electrodes 107, because the surface of the ceramic body 102 without the baked external electrodes 105 formed is protected by the inorganic substance layer 103, portions of the ceramic body 102 just below outer edges of the baked external electrodes 105 will not be eroded by plating solutions, or plated films will not adhere to the surface of the ceramic body 102.
In addition, the ceramic electronic component (chip circuit component) 400 described in JP 6-290989 A is manufactured by the following method.
First, a chip ceramic body 201 is prepared as shown in FIG. 8A.
Next, as shown in FIG. 8B, a resist 202 such as a maskant ink is applied to end surfaces of the ceramic body 201 by means such as, for example, a dip method, and subjected to curing.
Next, in this condition, the ceramic body 201 is put in a vacuum deposition system, and as shown in FIG. 8C, a protective film material is deposited over the entire surface to form a protective film 203. This protective film 203 is an amorphous thin film composed of an inorganic substance such as, for example, amorphous aluminum oxide, silicon oxide, or zirconium oxide. It is to be noted that the protective film 203 can be also formed by spray pyrolysis methods, chemical vapor deposition (CVD), and sputtering methods, besides physical vapor deposition methods.
Next, the resist 202 on the both ends of the ceramic body 201 is removed as shown in FIG. 8D. Thus, the protective film 203 over the end surfaces of the ceramic body 201 is also removed along with the resist 202, and the protective film 203 is left only on both side surfaces and top and bottom surfaces of the ceramic body 201.
Next, as shown in FIG. 8E, a conductive paste such as an Ag paste is applied by means such as a dip method to both ends of the ceramic body 201 with the protective film 203 formed, which have no protective film 203 provided, and baked to form baked external electrodes (conductor films) 204.
Next, as shown in FIG. 8F, Ni plated external electrodes (conductor films) 205 are formed on the surfaces of the baked external electrodes 204.
Finally, as shown in FIG. 8G, Sn plated external electrodes (conductor films) 206 are formed on the surfaces of the Ni plated external electrodes 205 to complete the conventional ceramic electronic component 400. It is to be noted that solder-plated external electrodes may be adopted in place of the Sn plated external electrodes 206.
In the formation of the Ni plated external electrodes 205 and the formation of the Sn plated external electrodes 206, because the surface of the ceramic body 201 without the baked external electrodes 204 formed is protected by the inorganic substance layer 203, portions of the ceramic body 201 just below outer edges of the baked external electrodes 204 will not be eroded by plating solutions, or plated films will not adhere to the surface of the ceramic body 201.
The prior art mentioned above has the following problems.
First, the method described in JP 5-251210 A requires the extra step of forming the insulating inorganic layer 103 over the entire surface of the fired ceramic body 102 as shown in FIG. 7C. This inorganic substance layer 103 has to be formed by a physical vapor deposition method (PVD method) or a chemical vapor deposition method (CVD method), such as a vacuum deposition method, a sputtering method, or an ion plating method, and the formation has the problems of cumbersome manufacture, increased length of manufacturing time, and increased cost.
In addition, while large numbers of products are manufactured simultaneously in mass production processes, the inorganic substance layer 103 of oxide or glass is formed over the entire surface of the ceramic body 102 in the method described in JP 5-251210 A, and there is thus a possibility that a plurality of ceramic bodies 102 will adhere to each other, or the ceramic body 102 will adhere to a firing tool, e.g., when the glass paste 104 is baked onto the ceramic body 102 to form the baked external electrodes 105. More specifically, there has been a possibility of decreasing the yield.
Moreover, in the method described in JP 5-251210 A, the melted inorganic substance layer 103 is absorbed by the inorganic binder in the glass paste 104 when the glass paste 104 is baked onto the ceramic body 102 to form the baked external electrodes 105 as shown in FIG. 7E, and in this case, there is a possibility that the composition of the inorganic binder will be altered to result in an excess reaction with the ceramic body 102, or glass layers will be formed on the surfaces of the baked external electrodes 105 formed. More specifically, there is a possibility that new defective products will be generated due to the altered composition of the inorganic binder.
On the other hand, the method described in JP 6-290989 A requires the step of applying the resist 202 such as a maskant ink by means such as a dip method as shown in FIG. 8B, the step of curing the applied resist 202, the step of forming the protective film 203 over the entire surface of the ceramic body 201 by a physical vapor deposition method, a spray pyrolysis method, a chemical vapor deposition (CVD), a sputtering method, or the like, as shown in FIG. 8C, the step of removing the resist 202 on the both ends of the ceramic body 201 as shown in FIG. 8D, etc., and has the problems of cumbersome manufacture, increased length of manufacturing time, and increased cost.